A conventional battery, such as a conventional chemical car battery, contains: a first set of electrodes of a first material; a second set of electrodes of a second material; and an acidic fluid in which these two electrodes are immersed to produce an electrical path between these two electrodes. These two sets of electrodes are selected to have significantly different electrochemical work functions W.sub.1 and W.sub.2, so that, when an external current path is provided between these two electrodes, a current is produced from the first electrode, through this external conductive path to the second electrode. This type of battery provides a peak voltage that is substantially equal to the difference between the electrochemical potentials of these two electrodes. The lifetime of conventional batteries is relatively short, because chemical energies are relatively small. Therefore, cars include generators that are powered by means of a first fan belt that is driven by the car's gasoline motor. These generators are connected to the battery by electrical leads that maintain the battery's stored chemical energy.
Many applications require batteries that have extremely long lifetimes. For example, space probes that will travel for many years before reaching their destinations, need to utilize batteries that have extremely long lifetimes. Similarly, many devices, such as computers, are connected to power sources that are designed to protect that device from power spikes in power lines to which these devices are connected. These devices also typically include batteries that contain at least enough stored energy that the computer has time to shut down in a manner that saves unstored data that has been keyed into this computer. It would be advantageous for these devices to have enough stored energy to power the computer for a day or even a few days which should be sufficiently long for the power company to correct its power distribution problem. These batteries would also be useful in smoke detectors, so that lives are not put at risk because the smoke detector's batteries lost their stored electrochemical energy. It is of crucial importance to have extremely long life batteries in space probes and any other application in which it is difficult or impossible to replace the batteries. However, even in applications in which it is merely inconvenient to have a battery go dead, it is advantageous to have long-life batteries, because such batteries need be replaced only at very long intervals.
FIG. 1 illustrates a battery 10 that is taught in U.S. Pat. No. 5,087,533 by Paul M. Brown, entitled Contact Potential Difference Celle that was issued on Feb. 11, 1992. Battery 10 contains: (1) a first electrode 11 that has a first work function W.sub.1 ; (2) a second electrode 12 that has a second work function W.sub.2 that is larger than W.sub.1, and (3) two or more nonconductive spacers 13 that keep electrodes 11 and 12 at a fixed spacing to produce a cavity 14 in which a gas or solid is ionized by a flux of radiation that has sufficient energy to ionize molecules or atoms in this radioactive material. This radiation flux can be provided by a variety of sources, such as a nuclear reactor, an external block of radioactive material or radioactive material within this battery. This radioactive material can be provided in several forms, such as: a gas, a liquid, a gel or a solid.
Because the work function of electrode 12 is larger than the work function of electrode 11, when one or more electric conductors 15 are connected between electrode 11 and electrode 12, a negative charge is produced on electrode 11 and an equal positive charge is produced on electrode 12. The resulting electropotential difference between these two electrodes is equal to the difference between the work functions of these two electrodes. This electropotential difference produces an electric field E that extends from electrode 12 to electrode 11. Free electrons and negative ions in cavity 14 are drawn toward the more lectropositive electrode (i.e., electrode 11) and the positive ions are drawn toward the more lectronegative electrode (i.e., electrode 12). The total current I between electrodes 11 and 12 is the sum of the electron current I.sub.e and the total ion currents I.sub.i.
This current flux experiences negligible resistance within the battery, because the density of ions and free electrons within cavity 14 is so low, that there is negligible scattering among these electrons and free ions. The small number of collisions between the electrons, ions and neutral particles in cavity 14 produces an extremely low level of excited states that can radiate away small amounts of energy. Therefore, resistive losses are extremely small compared to resistive losses in conventional batteries. Thus, these batteries not only exhibit extremely long half-lives (e.g., 458 years for Americium-241), they also exhibit extremely low heat dissipation rates. When a radioactive gas is supplied to cavity 14, the resulting positive and negative ions injected into the cavity by radioactive decays have sufficient energy to ionize a significant fraction of the gas ions within this cavity. Because the radioactive decay energies are typically on the order of millions of electron volts, the energy needed to ionize an atom that is impacted by a radioactive decay product is only a few electron volts (on the order of 32 eV), each radioactive ion can ionize on the order of a million gas molecules. This battery therefore exhibits an incredibly long lifetime, compared to electrochemical batteries.
Unfortunately, the metallic electrodes in this prior art battery are bulky, which significantly reduces this battery's efficiency and increases its weight. In addition, its design is not amenable to the integrated circuit processes that enable the manufacture of circuits to be produced in small size and/or to be produced inexpensively by these integrated circuit processes.
FIG. 2 illustrates a prior art battery 20 that consists of a series stack of N (=7) battery cells 10 of the type presented in FIG. 1. Battery 20 therefore provides a potential difference of N.multidot.(W.sub.1 -W.sub.2) across a resistor 21 of resistance R. Each of battery cells 10 exhibits an inherent resistance r, so the total resistance of the closed conductive path from the top of layer 11, through layers 12 and 13 back to the top of layer 11 is N.multidot.r+R. Therefore, the current I in this closed circuit is equal to N.multidot.(W.sub.1 -W.sub.2)/(N.multidot.r+R).
U.S. Pat. No. 5,246,505 entitled "System and Method To Improve the Power Output and Longevity of a Radioisotope Thermoelectric Generator" issued to Alfred Mowery, Jr. on Sep. 21, 1993 discloses an electrical power source that uses waste heat that is produced by radioactive decays of a highly radioactive material, such as plutonium. The energy in these nuclear decay products is converted into heat that is then converted into electrical energy by conventional methods, such as thermocouples that are distributed around the plutonium source. Unfortunately, the amount of heat involved is so large that the expensive process of helium outgassing is used to cool the radioactive source so that the thermal degradation does not severely degrade apparatus lifetime. Unfortunately, this thermoelectric generator exhibits the disadvantages of the conventional thermoelectric generator designs--namely: very low energy conversion efficiency, expensive manufacture, a large, heavy structure and substantial shielding to prevent health risks caused by the use of a plutonium source, which not only is radioactive, but is also very toxic.
U.S. Pat. No. 5,280,213 entitled "Electric Power Cell Energized By Particle And Electromagnetic Radiation", issued to John Day on Jan. 18, 19945 discloses a power cell that attenuates incident ionization radiation with material that emits slow secondary electrons that charge metallic plates of a capacitor of the type that has a pair of metal plates that are separated by a dielectric material. Although this device exhibits a multiplication factor, the inclusion of dielectric material in a pulsed mode of operation produces significant recombination within the secondary emitter, thereby significantly reducing efficiency.
U.S. Pat. No. 5,605,171 entitled "Porous Silicon With Embedded Tritium As A Stand Alone Prime Power Source For Optoelectronic Applications" discloses a radioluminescent apparatus that is coupled to a photovoltaic cell in which decay energy is converted into light energy. This light energy is then converted by a solar cell into electricity. Although this type of solar cell is fairly reliable, this type of cell has a relatively low energy conversion efficiency, because of its indirect method of energy conversion.
U.S. Pat. No. 5,616,928 entitled "Protecting Personnel And The Environment From Radioactive emissions By Controlling Such Emissions And Safely Disposing Of Their Energy", that was issued to Virginia Russell on Apr. 1, 1997, discloses a converter in which a radioactive source is enclosed within an enclosure formed of metal plates that are separated by dielectric material that forms a capacitive housing that is charged by decay particles. Unfortunately, space charge effects and reverse leakage currents limit the efficiency of this class of embodiments.
U.S. Pat. No. 5,642,014 entitled "Self-Powered Device issued to Steven Hillenius on Jun. 24, 1997 discloses a pn-junction type of isotopic electric converter. This generator includes an integrated circuit that is powered by this converter. This converter is a pn junction type of isotopic converter. This pnjunction is adjacent to a tritium-containing layer that provides .beta.-particles that penetrate the depletion layer and produce electron-hole pairs therein. These electron-hole pairs are separated by the electric field within the depletion layer, thereby producing a current. Unfortunately, like all converters that utilize a pn junction for electrical conversion, the fragile crystalline structure of the semiconductor device is quickly damaged by the bombarding .beta. particles. This eventually destroys this semiconductor device to an extent that severely degrades conversion efficiency. Although such degradation can be slowed by annealing the junction, the rate of degradation of this type of device limits its cost-effectiveness.
Unfortunately, none of the devices can provide increased power generation during intervals of peak power demand. This means that these electrical power generators operate at a level significantly below its peak power level most of the time.
Of the devices discussed above, that convert radioactive decay energy into electricity, none of them has succeeded commercially, because of the deficiencies discussed above. However, because the radioactive decay rate for each of these devices is relatively low, each of these electric power sources provides current at a level that is substantially constant over the time intervals during which most power generators operate.